Add a mimeHandler extension API.

extensions/common/api/schemas.gypi

 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 {
   'sources': [
     '<@(schema_files)',
   ],
   'variables': {
     'chromium_code': 1,
@@ skipping 10 matching lines @@
       'cast_channel.idl',
       'copresence_endpoints.idl',
       'dns.idl',
       'events.json',
       'extensions_manifest_types.json',
       'extension_options_internal.idl',
       'extension_types.json',
       'guest_view_internal.json',
       'management.json',
       'hid.idl',
+      'mime_handler_private.idl',
       'mime_handler_view_guest_internal.json',
       'mojo_private.idl',
       'power.idl',
       'printer_provider.idl',
       'printer_provider_internal.idl',
       'runtime.json',
       'serial.idl',
       'socket.idl',
       'sockets_tcp.idl',
       'sockets_tcp_server.idl',
@@ skipping 24 matching lines @@
         'schema_files': [
           '<@(chromeos_schema_files)',
         ],
       }]
     ],
     'cc_dir': 'extensions/common/api',
     'root_namespace': 'extensions::core_api::%(namespace)s',
     'impl_dir_': 'extensions/browser/api',
   },
 }